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Prior to. Unit IX. Four-Stroke cycle. 1. Look at the pictures and describe the position of the piston during the cycle using linking words: first, then, after that, in the end
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prior to
2. External combustion engines needed steam which pushed the piston.
in order to
3. During the compression stroke the piston ascends.
moves upward
| I 1 moves 2 compresses 3 combustion 4 this 5 mixture 6ignited 7 expand | II. 1 is, 2+, 3+, 4a, 5to, 6 for, 7+, 8a III. 1a, 2b, 3b, 4a, 5b | IV. 1 operate, 2 piston, 3 are, 4 crankshaft |
| V. 1. Steam engine was invented prior to gasoline engine. 2. External combustion engines needed steam in order to push the piston. 3. During the compression stroke the piston moves upward. | ||
UNIT IX. FOUR-STROKE CYCLE
1. Look at the pictures and describe the position of the piston during the cycle using linking words: first, then, after that, in the end
2. Read the text and choose the most suitable heading for each of the numbered paragraphs. There is one extra heading
a. Principle of operation.
b. The main elements of an internal combustion engine.
c. Gasoline powered engines
d. The inventor of the internal combustion engine.
Otto cycle engine
1_________________________________________
Internal combustion engine is a heat engine. It produces power by burning fuel inside a closed space. Many scientists claimed the invention of the internal combustion engine in the 1860s, but only one engineer, Nikolaus August Otto, got the patent on the four- stroke engine in 1867. He developed the four-stroke Otto cycle, which is widely used in transportation even today.
2__________________________________________
The principal parts of an internal combustion engine are a cylinder, a cylinder head, a piston, a connecting rod, a crankshaft, an intake valve, an exhaust valve and a spark plug.
3__________________________________________
A four-stroke engine needs four strokes of the piston to complete one cycle.
During the intake stroke the piston is at the top dead center. The crankshaft turns and pulls down the piston. The piston draws the explosive mixture of air and fuel behind it.
During the compression stroke the piston is at the bottom dead center. The crankshaft turns, pushes the piston upwards and compresses the combustible mixture to a high pressure and temperature.
During the power stroke the combustible mixture is ignited by an electric spark. The hot gases push the piston down. The work is done.
During the exhaust stroke the burnt gases are driven out of the cylinder through the exhaust valve.
3. Read the text and choose the most suitable word underlined in the sentences
On the compression stroke the piston is pulled/pushedinside/outside the cylinder, compressing the fuel-air mixture into a smaller and smaller space. The compression of the mixture against the top of the cylinder causes the air to heat up, which/who in turn heats the mix/ mixture. Compression of the fuel-air mixture also makes iteasier/more easy to ignite and makes the resulting explosion more powerless/powerful. There is less/least space for the expanding gases of the explosion to flow, which means they will push/pull harder against the piston inorder to/because of escape. At the top of the compression stroke, the fuel-air mixture is ignited by a spark from a spark plug locating/located in the cylinder head, causing an explosion that pushes the piston down/leftward. These/this stroke is called the power stroke, it turn/turns the crankshaft.
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4. Look through the short texts and guess the meanings of the underlined words. Match the description of strokes and the pictures. Explain your choice
| 1. Suction (intake) stroke: During this stroke, the piston starts its motion from the top downward of the cylinder. Synchronously, the intake valve is opened, allowing air-fuel mixture to enter to the combustion chamber. | a 
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| 2. Compression stroke: In this one, both valves should be closed. The piston starts to move upward to compress the fuel, until it reaches the top dead center. By compressing the fuel, the fuel temperature and pressure increases. | b 
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| 3. Power stroke: As the piston reaches the top dead center, the spark plug ignites a spark, allowing the fuel to burn. The combustion results in a high power that is transmitted through the crank mechanism. Both valves are closed. | c 
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| 4. Exhaust stroke: After reaching the bottom dead center the piston starts back upward motion to drive the exhaust gases out of the cylinder. The exhaust valve is opened to allow the gases to go outside the cylinder. |
d 
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